Zeolite-based catalyst material, the preparation thereof and the use thereof for the selective dehydrogenation of N-butane

ABSTRACT

A process in which a hydrocarbon feedstock containing n-butane is selectively dehydrogenated to a product containing butenes. A catalyst suitable for the selective dehydrogenation of a feedstock containing n-butane to provide a product containing butenes. A method for producing a catalyst suitable for the selective dehydrogenation of a feedstock containing n-butane to provide a product containing butenes.

This application is a division of application Ser. No. 09/222,446, filedDec. 29, 1998, now U.S. Pat. No. 6,218,328.

FIELD OF THE INVENTION

The invention relates to a catalyst suitable for the selectivedehydrogenation of n-butane, a process for the preparation of a catalystsuitable for the selective dehydrogenation of n-butane and the use ofthis catalyst in a process for the selective dehydrogenation ofn-butane.

BACKGROUND OF THE INVENTION

It is known that n-butane can be dehydrogenated to butenes in thepresence of variety of catalyst supports impregnated with a variety ofmetals. The dehydrogenation often produces coke at a rate that spoilsthe reactivity of the catalyst in a sufficiently short period of time torender the commercial use of the catalysts infeasible. A catalystcomposition has newly been found to be useful for selectivelydehydrogenating n-butane to butene products without producing coke at acommercially inhibiting rate.

SUMMARY OF THE INVENTION

It is an object of this invention to at least partially dehydrogenaten-butane to butenes.

Another object of this invention is to provide an improved zeolite-basedcatalyst that can be utilized in the dehydrogenation of n-butane tobutenes.

A further object of this invention is to provide a method for making azeolite-based catalyst that can be utilized in the dehydrogenation ofn-butane to butenes.

A still further object of this invention is to accomplish thedehydrogenation of n-butane while minimizing the co-production of coke.

The invention is a zeolite-based catalyst in which an L-type zeolitethat has been modified with titania is impregnated with platinum and tinto provide a catalyst composition and a process in which a feedstockcontaining n-butane is passed in contact with this catalyst compositionunder selective dehydrogenation conditions to yield butenes as productwhile minimizing the co-production of coke.

Other objects and advantages of the invention will become apparent fromthe detailed description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The zeolite material used in making the inventive compositions can beany zeolite which when contacted with a feedstock containing n-butaneunder suitable operating conditions is effective in the conversion ofn-butane to butenes. Preferably, the zeolite is of type L and morepreferably is an LTL zeolite (as defined in ATLAS OF ZEOLITE STRUCTURETYPES, W. M. Meier and D. H. Olson, Butterworth-Heinemann, Third RevisedEdition 1992). The preferred type of zeolite is described as Linde TypeL, K₆Na₃ [Al₉Si₂₇O₇₂]·21H₂O.

The catalyst compositions described herein also contain an inorganicbinder (also called matrix material) preferably selected from amongalumina, silica, alumina-silica, aluminum phosphate, clays (such asbentonite) and mixtures thereof. The content of the zeolite component ofthe mixture of zeolite and inorganic binder is about 50-99 (preferablyabout 50-80) weight percent. The content of the above-listed inorganicbinders in the mixture of zeolite and inorganic binder is about 1-50weight percent. Generally, the zeolite and organic binder components arecompounded and subsequently shaped (such as by pelletizing, extruding ortableting). Generally the surface area of the compounded composition isabout 50-700 m²/g, and the particle size is about 1-10 mm. Thecompounded zeolite composition can be subjected to heat treating asdescribed below.

In the preferred embodiment of this invention the type L zeolite isadmixed with bentonite, Al₂(OH)₅Cl·5H₂O and water and thoroughly blendedto form a paste which is then extruded, pelleted, dried in air to form azeolite composition suitable for use as catalyst in the dehydrogenationof n-butane.

This zeolite composition can then be subjected to a heat treatment,following the conditions set out below, before being used in thepreparation of a catalyst by the preferred embodiment of this invention.In the heat treatment, the zeolite composition is exposed, by anysuitable method known in the art, to a gas atmosphere under temperatureand pressure conditions and for a period of time that is suitable toprovide a desired heat treated product.

The gas used in the heat treatment of the zeolite composition can beselected from the group consisting of inert gases (nitrogen, helium,argon and the like), reducing gases (carbon monoxide, hydrogen and thelike), air, oxygen and steam. The preferred gas is selected from amongair, oxygen, nitrogen, steam and mixtures thereof. Most preferably, thetreatment gas is selected from among air, oxygen, nitrogen and mixturesof two thereof.

Generally, this heat treatment can be conducted at a pressure in a rangefrom below atmospheric pressure to about 1000 pounds per square inchabsolute (psia). More typically, however, the pressure range is fromabout atmospheric to about 100 psia. The temperature of this heattreatment is generally in the range of about 250° C. to about 800° C.Preferably, this temperature range is from about 350° C. to about 700°C. and, most preferably, the temperature of this heat treatment is in arange of about 450° C. to about 600° C.

The time period for conducting this heat treatment must be sufficient toprovide a material that is substantially dry, i.e., free of water.Generally, the period of time during which the zeolite is exposed totreating gas at appropriate conditions of temperature and pressure canrange from about 0.1 hour to about 30 hours. Preferably, this heattreatment is conducted for a time period in the range of about 0.25 hourto about 20 hours and, most preferably, from about 0.5 hour to about 10hours.

Addition of Titanium

The zeolite composition is further treated to provide a zeolitecomposition containing titanium. Titanium is incorporated into thezeolite composition to form a mixture of the zeolite composition andtitanium. The titanium can be incorporated into the zeolite by anysuitable means or method known in the art for incorporating metallicelements into a substrate material. One method is to mix the zeolitecomposition with at least one anhydrous compound, followed by a heattreatment preferably at about 700-800° C. for about 1-10 hours in aninert gas stream. Another method, presently preferred for impregnatingthe zeolite composition, uses a liquid impregnation solution containinga concentration of titanium sufficient to ultimately provide the finalinventive composition with the concentration of titanium in the requiredrange.

When titanium is incorporated into the zeolite composition with anaqueous solution of a titanium compound, the preferred impregnationsolution is an aqueous solution of titanium ethoxide. Thetitanium-impregnated zeolite composition is then heat treated,preferably at about 400-700° C. for about 1-10 hours in an inert gasstream. The titanium-impregnated zeolite composition is then calcined inan oxidizing atmosphere, preferably at about 400-700° C. for about 1-10hours to produce a titania-impregnated zeolite composition.

Any water soluble titanium compound is suitable for use in theimpregnation of the zeolite in this invention. Suitable titaniumcompounds include, but are not limited to, titanium halides, tetraalkyltitanates of the general formula Ti(OR)₄ wherein each R is an alkylgroup (such as tetraethyl titanate, tetraisopropyl titanate, tetrabutyltitanate), titanium methoxide and titanium ethoxide. At present,titanium ethoxide is preferred.

The amount of titanium incorporated or impregnated into the zeoliteshould provide a concentration effective to assure predetermined buteneconversion yields employing the catalyst composition in the selectivedehydrogenation of feedstock that contains n-butane. Generally, theweight percent of titanium present both in the titanium impregnatedzeolite composition and in the zeolite composition containing additionalmetal impregnants is in a range of about 0.001 to about 10 weightpercent of the impregnated zeolite composition. The preferredconcentration of titanium in both the titanium impregnated zeolitecomposition and in the zeolite composition containing additional metalimpregnants is in the range of about 0.01 to about 5 weight percent and,more preferably, from about 0.1 to about 2 weight percent.

The titanium impregnated zeolite composition is calcined to provide atitania-modified zeolite composition. The calcination process isconducted in an oxidizing atmosphere preferably in the presence ofoxygen or air although a non-interfering amount of a carrier gas inertto the oxidation process can also be present. This heat treatment can beconducted at a pressure in a range from below atmospheric pressure toabout 1000 pounds per square inch absolute (psia), more typically fromabout atmospheric to about 100 psia. The temperature of this heattreatment is generally in the range of about 250° C. to about 800° C.Preferably, this temperature range is from about 350° C. to about 700°C. and, most preferably, the temperature of this heat treatment is in arange of about 450° C. to about 600° C. The period of time during whichthe zeolite is exposed to treating gas at appropriate conditions oftemperature and pressure can range from about 0.1 hour to about 30hours, preferably, from about 0.25 hour to about 20 hours and, mostpreferably, from about 0.5 hour to about 10 hours.

Addition of Platinum and Tin

After the heat treatment the titania-modified zeolite composition isfurther treated to provide a catalyst composition containing platinumand tin. Both platinum and tin are incorporated into thetitania-modified zeolite composition to form a mixture oftitania-modified zeolite, platinum and tin. The platinum and tin can beincorporated into the titania-modified zeolite composition by anysuitable means or method known in the art for incorporating metallicelements into a substrate material. One method is to mix thetitania-modified zeolite composition with at least one anhydrouscompound, followed by a heat treatment preferably at about 700-800° C.for about 1-10 hours in an inert gas stream. Another method, presentlypreferred for impregnating the titania-modified zeolite composition,uses a liquid impregnation solution containing a concentration ofplatinum and tin sufficient to ultimately provide the final inventivecomposition with the concentration of platinum and tin in the requiredrange.

Generally, any platinum-containing compound can be employed in theprocess of this invention. Examples of suitable platinum compoundsinclude, but are not limited to, chloroplatinic acid, platinic chloride,platinum bromide, platinum iodide, tetramine platinum chloride,tetramine platinum nitrate, tetramine platinum hydroxide,tetrachlorodiamine platinum and combinations of any two or more thereof.

Any tin-containing compound can be employed in the process of thisinvention. Examples of suitable tin compounds include, but are notlimited to, stannous acetate, stannic acetate, stannous bromide, stannicbromide, stannous chloride, stannic chloride, stannous oxalate, stannoussulfate, stannic sulfate, stannous sulfide and combinations of any twoor more thereof.

When platinum and tin are incorporated into the titania-modified zeolitewith an aqueous solution of a platinum or a tin compound, the preferredimpregnation solution is an aqueous solution, preferably chloroplatinicacid for the impregnation with platinum, or an aqueous solution formedby dissolving a salt of tin, preferably hydrated stannous chloride(SnCl₂·2H₂O), in water. It is acceptable, however, to use a somewhatacidic solution to aid in the dissolution of the metal salt. Theplatinum-and tin-impregnated, zeolite is then heat treated, preferableat about 400-700° C. for about 1-10 hours in an inert gas stream.

The amount of platinum and tin incorporated or impregnated into thezeolite should provide a concentration effective to assure predeterminedbutene conversion yields employing the catalyst composition in theselective dehydrogenation of feedstock that contains n-butane.Generally, the weight percent of platinum or tin present in theimpregnated zeolite is in a range of about 0.001 to about 10 weightpercent of the impregnated zeolite composition. The preferredconcentration of platinum or tin in the impregnated zeolite is in therange of about 0.01 to about 5 weight percent and, more preferably, fromabout 0.1 to about 2 weight percent of the impregnated zeolitecomposition.

Generally, this heat treatment can be conducted at a pressure in a rangefrom below atmospheric pressure to about 1000 pounds per square inchabsolute (psia). More typically, however, the pressure range is fromabout atmospheric to about 100 psia. The temperature of this heattreatment is generally in the range of about 500° C. to about 1000° C.Preferably, this temperature range is from about 600° C. to about 900°C. and, most preferably, the temperature of this heat treatment is in arange of about 650° C. to about 850° C.

Generally, the period of time during which the zeolite is exposed totreating gas at appropriate conditions of temperature and pressure canrange from about 0.1 hour to about 30 hours. Preferably, this heattreatment is conducted for a time period in the range of about 0.25 hourto about 20 hours and, most preferably, from about 0.5 hour to about 10hours and results in a calcined, steam treated product suitable for usein a catalyst bed.

The process of this invention applies most specifically to theconversion of n-butane to butenes. The feedstock can be any feedstockthat contains n-butane. The higher the content of n-butane the morepreferred is a feedstock for this invention. Among the feedstocks forwhich this invention is useful are those having a content of crackedhydrocarbon feedstocks from the catalytic cracking (e.g., fluidizedcatalytic cracking and hydrocracking) of gas oils and the thermalcracking of light hydrocarbons, naphthas, gas oils, reformates andstraight-run gasoline. The cracked gasoline feedstock generallycomprises hydrocarbons containing 2-16 carbon atoms per molecule chosenfrom among paraffins (alkanes) and/or olefins (alkenes) and/ornaphthenes (cycloalkanes). A more preferred feedstock for the process ofthis invention is a cracked gasoline derived from the fluidizedcatalytic cracking of gas oil, suitable for use as at least a gasolineblend stock generally having a boiling range of from about 80° F. toabout 430° F. The boiling range of the cracked hydrocarbon feedstock isdetermined by the standard ASTM method for measuring the initial boilingpoint and the end-point temperatures. Generally the content of paraffinsexceeds the combined content of olefins, naphthenes, and aromatics (ifpresent).

Feedstock containing n-butane and the catalyst compositions can becontacted within a reaction zone in any suitable manner. The contactingcan be operated with a catalyst bed in a reactor vessel as a batchprocess or, preferably, as a continuous process. In either a batch or acontinuous process a solid catalyst bed can be employed. Both the batchand continuous modes of operation have known advantages anddisadvantages so that one skilled in the art can select the mode mostsuitable for a particular feedstock to be contacted with the inventivecatalyst arrangement.

Contacting the feedstock containing n-butane and the catalystcomposition is carried out in a reaction zone containing the catalystcompositions while employing reaction conditions that promote thedehydrogenation of n-butane with the formation of butenes. The reactiontemperature employed in the contacting is in the range of from about300° C. to about 800° C., preferably, from about 400° C. to about 700°C. and, more preferably, from 500° C. to about 600° C. The pressureemployed in the contacting can range from subatmospheric up to about 500psia and, preferably, from about atmospheric to about 400 psia.

The flow rate at which the cracked hydrocarbon feedstock is charged tothe conversion reaction zone for contact with the catalyst compositionis selected to provide a weight hourly space velocity (WHSV) in a rangehaving an upward limit of about 1000 hour⁻¹. The term “weight hourlyspace velocity”, as used herein, shall mean the numerical ratio of therate at which a cracked hydrocarbon feedstock is charged to theconversion reaction zone in pounds per hour divided by the pounds ofcatalyst contained in the conversion reaction zone to which thehydrocarbon is charged. The preferred WHSV of the feed to the conversionreaction zone, or contacting zone, can be in the range of from about0.25 hour⁻¹ to about 250 hour⁻¹ and, more preferably, from about 0.5hour⁻¹ to about 100 hour⁻¹.

The following examples are presented to further illustrate thisinvention and are not to be construed as unduly limiting its scope.

EXAMPLE I

This example illustrates the preparation of catalysts which weresubsequently tested as catalysts in the selective dehydrogenation ofn-butanes to butenes.

Catalyst A (Control)—LTL Zeolite Impregnated with Platinum and Tin.

A quantity of 400 gm of commercially available LTL-K zeolite catalystprovided by C. U. Chemie Euticon A. G., a Swiss corporation, under theirproduct designation “L-Zeocat” was admixed with 12.0 gm of Bentonite,48.0 gm of Al₂(OH)₅Cl·5H₂O and 216 g of water. The mixture was blendermixed into a paste and extruded into {fraction (1/16)} inch pelletswhich were air dried at 125° for 3 hours and then calcined at 500° C.for 3 hours to yield an alumina-bound zeolite catalyst.

A 37 percent solution of HCl in water was added to a mixture ofchloroplatinic acid and hydrated tin chloride (SnCl₂·2H₂O) to form asolution having 1 wt percent of chloroplatinic acid, 0.65 wt percent oftin chloride, 8.35 wt percent HCl and 90 wt percent water.

A quantity of 50 gm of the alumina-bound zeolite catalyst was admixedwith an 11.1 gm quantity of the aqueous solution containing platinum andtin. The impregnated zeolite was dried and calcined with air flow at atemperature of 538° C. for 6 hours to produce 20.0 gm of alumina-boundzeolite impregnated with 0.21 wt. percent platinum and 0.15 wt. percenttin.

Catalyst B and C (Invention)—Titania-modified LTL Zeolite Impregnatedwith Platinum and Tin.

A quantity of 10.0 g of the alumina-bound zeolite catalyst produced forCatalyst A was admixed with 5.56 g of a 3 wt percent aqueous solution oftitanium ethoxide and calcined for 6 hours at 538° C. to provide 9.43 gof titania-modified alumina-bound zeolite.

A quantity of 6.05 g of the aqueous solution containing platinum and tinproduced for Catalyst A was admixed with the 9.43 g of titania-modifiedalumina-bound zeolite produced above and calcined at 538° C. for 6 hoursto yield 9.25 g of titania-modified alumina-bound zeolite impregnatedwith 0.25 wt percent platinum and 0.22 wt percent tin.

EXAMPLE II

This example illustrates the use of the Zeolite materials described inExample I as catalysts in the selective dehydrogenation of n-butane tobutenes.

For each of the test runs, a 3.0 g sample of the catalyst materialsdescribed in Example I was placed into a stainless steel tube reactor(length: about 18 inches; inner diameter: about 0.5 inch). An n-butanefeedstock was passed through the reactor at a flow rate of about 5 WHSV,at a temperature of about 550° C. and at atmospheric pressure (about 0psig). The runs using Catalysts A and B were done without use of acarrier gas. Hydrogen at a rate of 18.6 L/hr and a mol ratio of hydrogento hydrocarbon of about 3 was used a carrier gas for the run usingCatalyst C. The formed reaction product exited the reactor tube andpassed through several ice-cooled traps. The liquid portion remained inthese traps and was weighed. The volume of the gaseous portion whichexited the traps was measured in a “wet test meter”. Liquid and gaseousproduct samples (collected at hourly intervals) were analyzed by meansof a gas chromatograph. Results of the test runs for Catalysts A throughC are summarized in Table 1. All test data were obtained up to about 7hours on stream except for Catalyst A which was obtained up to about 6hours on stream.

TABLE I Ti PT Sn H₂/n-C₄ n-Butane Butenes Coke Catalyst Wt %¹ Wt %¹ Wt%¹ Mol Ratio Wt % Conv. Wt % Prod. Avg. Wt %/hr A (Cont.) 0.000 0.2110.146 0.000 20.668 17.149 0.282 B (Inv.) 0.144 0.249 0.244 0.000 30.07924.839 0.106 C (Inv.) 0.144 0.249 0.244 3.000 23.102 20,696 0.025 ¹Wt %of composition

The tests show that Catalyst A (Control), an LTL zeolite impregnatedwith platinum and tin, was not as efficient in the selectivedehydrogenation of n-butane to butenes as Catalysts B and C (Invention),a titania-modified LTL zeolite impregnated with platinum and tin. Theinventive catalyst was used in the selective dehydrogenation of n-butaneboth without using hydrogen as a co-feed in the dehydrogenation (withCatalyst B) and with hydrogen as a co-feed in the dehydrogenation (withCatalyst C). The dehydrogenation employing catalyst without titaniamodification converted a lesser weight percentage of the n-butane andproduced a lesser weight percentage of butenes with a greater averagehourly production of coke than employing the titania-modified zeoliteeither with or without hydrogen co-fed to the dehydrogenation. Thetitania-modified zeolite converted a greater weight percentage ofn-butane in the feedstock to a greater weight percentage of butenes inthe product while producing a better than satisfactory average amount ofcoke per hour. Although the use of hydrogen co-feed reduced the cokeproduction, as expected, the n-butane conversion and butenes productionwere less than without the hydrogen co-feed. The relatively low cost ofoperation without using the hydrogen co-feed makes the platinum and tinimpregnated titania-modified zeolite very attractive as catalyst for theselective dehydrogenation of n-butane.

Reasonable variations, modifications and adaptations can be made withinthe scope of the disclosure and the appended claims without departingfrom the scope of this invention.

That which is claimed is:
 1. A method for dehydrogenating n-butane tobutenes comprising, under conditions for the production of butenescontacting n-butane with a catalyst prepared by the method comprising:(A) admixing LTL zeolite, aluminum hydroxychloride and Bentonite toprovide an LTL zeolite composition and (B) calcining the LTL zeolitecomposition to provide a calcined LTL zeolite composition; (C) addingtitanium to the calcined LTL zeolite composition by impregnating with atitanium compound to provide a titanium-modified LTL zeolitecomposition; (D) calcining the titanium-modified LTL zeolite compositionto provide a titania-modified LTL zeolite composition and (E) addingplatinum and tin to the titania-modified LTL zeolite by impregnating thetitania-modified LTL zeolite composition with a platinum-tinimpregnating solution to provide a titania-modified LTL zeolitecomposition impregnated with platinum and tin.
 2. A method fordehydrogenating n-butane to butenes according to claim 1 wherein thetitanium compound is chosen from the group consisting essentially oftitanium halides, tetraalkyl titanates of the general formula Ti(OR)₄wherein each R is an alkyl group, titanium methoxide and titaniumethoxide.
 3. A method for dehydrogenating n-butane to butenes accordingto claim 2 wherein the titanium compound is titanium ethoxide.
 4. Amethod for dehydrogenating n-butane to butenes according to claim 2wherein the platinum compound is chosen from the group consistingessentially of chloroplatinic acid, platinic chloride, platinum bromide,platinum iodide, tetramine platinum chloride, tetramine platinumnitrate, tetramine platinum hydroxide, tetrachlorodiamine platinum andcombinations of any two or more thereof and the tin compound is chosenfrom the group consisting essentially of stannous acetate, stannicacetate, stannous bromide, stannic bromide, stannous chloride, stannicchloride, stannous oxalate, stannous sulfate, stannic sulfate, stannoussulfide and combinations of any two or more thereof.
 5. A method ofdehydrogenating n-butane to butenes according to claim 4 wherein theplatinum compound is chloroplatinic acid.
 6. A method of dehydrogenatingn-butane to butenes according to claim 4 wherein the tin compound isstannous chloride.
 7. A method for dehydrogenating n-butane to butenesaccording to claim 2 wherein the platinum compound is chloroplatinicacid and the tin compound is stannous chloride.